Gravity variations have been detected using suspended large masses on the order of kilograms. It was believed the masses had to be large because the force of gravity is the weakest known force. More recently, atom interferometry, and in particular, accelerometers utilizing interferometry have been proposed as gravitational probes. See, for example, B. M. Anderson, J. M. Taylor and V. M. Galitski, “Interferometry with synthetic gauge fields”, Physical Review A, 83, 031602(R), 2011.
These devices have practical limitations. The devices using large masses can only detect large variations in the gravitational field. There are a number of complex technical challenges to overcome so as to make interferometers practical for field operations. Some of these requirements include cooling and keeping atoms near absolute zero and removing unwanted inertial effects. Thus, it would be highly desirable to have a device that could detect relatively small gravity fluctuations, such as those due to density and subsurface stress changes in porous rocks relating to geologic features of interest, and which could be used conveniently at reasonable temperatures, such as room temperature.